This application is based on application No. 2000-378589 filed in Japan, the contents of which are hereby incorporated by reference.
This invention relates optical devices used for synthesizing multiple light components and for separating light into multiple light components. This invention also relates to projection display apparatuses and image capturing devices that include such an optical device.
In the field of optics, it is sometimes desirable to separate light into multiple light components or synthesize multiple light components to form a single ray of light. For example, image projectors are known that generate a light ray for each of a set of primary colors, such as red, green and blue, and then combine, using a color synthesizer, each of the primary color light rays into a single light ray for projection.
One type of known color synthesizer is a cross-dichroic prism that comprises four identical triangular prisms. The prisms are bonded together such that the cross-section of the bonded surfaces, which work as dichroic surfaces, have a letter X configuration. For this reason, cross-dichroic prisms are often referred to as xe2x80x9cx-cubesxe2x80x9d.
An example of a projection display apparatus that attains color synthesis using a cross-dichroic prism is disclosed in Japanese Patent Publication No. 8-16828. An optical system for this type of projection display apparatus, as shown in FIG. 5, comprises a light source 1, lens arrays 2a and 2b, reflection mirrors 3a and 3b, a superimposing lens 4, dichroic mirrors M1 and M2, a relay optical system 5, field lenses 6R, 6G and 6B, transmission-type light valves 7R, 7G and 7B, a cross-dichroic prism 15, and a projection lens 9 (having an optical axis AX) as well as other miscellaneous components. The spatial energy distribution of the light from the light source 1 is made uniform by an integrator means comprising the two lens arrays 2a and 2b and a superimposing lens 4. Between the two lens arrays 2a and 2b, the light path of the illuminating light is bent by the reflection mirror 3a. Where the light valves 7R, 7G and 7B are composed of liquid crystal, a polarization conversion means (not shown) is located near the integrator means in order to improve the efficiency of the use of the light from the light source 1.
The first and second dichroic mirrors M1 and M2 are color separating means that separate the illuminating light exiting the integrator means into red (R), green (G) and blue (B) light components. The R light component is reflected by the first dichroic mirror Ml, and, after it is reflected by the reflection mirror 3b, it passes through the field lens 6R. The G and B light components, on the other hand, pass through the first dichroic mirror M1. The G light component is reflected by the second dichroic mirror M2 and then passes through the field lens 6G. The B light component passes through the second dichroic mirror M2 and then passes through the relay optical system 5 comprising relay lenses 5a and 5c and reflection mirrors 5b and 5d as well as the field lens 6B.
Each field lens 6R, 6G and 6B has a power determined such that the light exiting the lens strikes the pupil of the projection lens 9. The R, G and B light components that have respectively passed through the field lenses 6R, 6G and 6B are modulated by the transmission-type light valves 7R, 7G and 7B that are provided near the field lenses 6R, 6G and 6B. The modulated R, G and B light components are chromatically synthesized by the cross-dichroic prism 15, which comprises a color synthesizer, and are then projected onto a screen (not shown) by the projection lens 9.
The cross-dichroic prism 15 that performs color synthesis of the R, G and B light components comprises four triangular prisms bonded to one another, as described above. The dichroic surfaces, the cross-sectional configuration of which forms a letter X, reflect only R and B light components and allow the G light component to pass through, resulting in color synthesis of the three colors. In the color synthesis, the R light component exiting the first light valve 7R, for example, is reflected by the first dichroic surface comprising two surfaces 15a and 15b. The fact that one dichroic surface 15a or 15b is defined by two different triangular prisms contributes to reduced precision in the manufacture of the cross-dichroic prism 15. For example, if the accuracy of bonding of the prisms is poor, one dichroic surface becomes defined by two surfaces 15a and 15b that are parallel to but offset from each other with the apex 15d of one of the prisms serving as a boundary, as shown in FIG. 6. In addition, if the precision in the processing of individual triangular prisms is poor, one dichroic surface becomes defined by two surfaces 15a and 15b that create an angle (180xc2x1"sgr")xc2x0 when measured with the apex 15d as the center, "sgr" representing the angular deviation from flatness created by the two surfaces, as shown in FIG. 7.
The same precision-reducing factors exist with the second dichroic surface that reflects the light exiting the third light valve 7B, as with the first dichroic surfaces 15a and 15b. When the light exiting the first and third light valves 7R and 7B is reflected by the first and second dichroic surfaces having reduced precision, respectively, partial mismatch occurs in the synthesis of the projected images from the individual light valves 7R, 7G and 7B. This mismatch cannot be adjusted by adjusting the positions of the light valves 7R, 7G and 7B relative to one another. If a cross-dichroic prism 15, including precision reducing factors caused during manufacture, is used for color synthesis as described above, limitation results in making the light valves 7R, 7G and 7B compact and delicate, in particular, due to concerns regarding precision. Furthermore, because manufacture ensuring high precision is required, the price of the product will also increase.
Another type of known color synthesizer, as illustrated in FIG. 8 and disclosed in Japanese Patent No. 2505758, is a dichroic prism 16. Color synthesizers such as dichroic prism 16 are often refered to as xe2x80x9cphilips-typexe2x80x9d prisms. The dichroic prism 16 has an optical axis AX and comprises three prisms P1, P2 and P3. The bonded surfaces of the first prism P1 and the second prism P2 define a first dichroic surface D1. In the third prism P3, the surface that opposes a prism surface T1 of the second prism P2 with a certain space therebetween comprises a second dichroic surface D2. The third prism P3 also has a prism surface T2, the significance of which will be discussed below. If a dichroic prism 16 (in FIG. 8) is used instead of the cross-dichroic prism 15 in the projection display apparatus described above with reference to FIG. 5, an optical construction shown in FIG. 9 results. In FIG. 9, identical or equivalent members to those in the projection display apparatus shown in FIG. 5 are indicated using the same numbers and letters.
The R light component undergoes total reflection by the prism surface T1, is reflected by the first dichroic surface D1, and is then synthesized with the G light component. The chromatically synthesized R and G light components strike the second dichroic surface D2. The B light component undergoes total reflection by the prism surface T2, followed by reflection by the second dichroic surface D2, and is synthesized with the R and G light components. The R, G and B light components synthesized by the two dichroic surfaces D1 and D2 exit through the prism surface T2, and are projected by the projection lens 9 onto a screen (not shown).
The dichroic prism 16 shown in FIG. 8 entails little reduction in precision during manufacturing because both of the first and second dichroic surfaces D1 and D2 are defined by a single prism surface. However, in comparison with the display apparatus shown in FIG. 5, if the optical construction of the display apparatus shown in FIG. 9 is such that illumination is carried out based on the same F-number while using transmission-type light valves 7R, 7G and 7B that are of the same size as those included in the apparatus shown in FIG. 5, the overall size of the illuminating system including the color separating means becomes large.
An object of the present invention is to provide an improved color synthesizing device.
Another object of the present invention is to provide an improved and inexpensive optical apparatus that is capable of performing color synthesis with a high degree of accuracy.
In order to attain these and other objects, a color synthesizer is provided that comprises first, second, and third prisms. The first prism has a first receiving surface for receiving the first light component from the first light valve, the second prism has a second receiving surface for receiving the second light component from the second light valve, and the third prism has a third receiving surface for receiving the third light component from the third light valve. The first prism also has a first exit surface for allowing the thus received first light component to pass from the first prism to the second prism, and the second prism has a first synthesizing surface for reflecting the thus received second light component while receiving the first light component from the first prism, thereby synthesizing the first and second light components. The second prism also has a second exit surface for allowing the thus synthesized first and second light components to pass from the second prism to the third prism, wherein the second light component is synthesized with the first light component before striking the second exit surface. The third prism has a second synthesizing surface for reflecting the third light component while receiving the synthesized first and second light components from the second prism, thereby synthesizing the first, second, and third light components. Finally, the third prism has a third exit surface for both reflecting the third light component and allowing the synthesized first, second, and third light components to exit from the color synthesizer.
In the color synthesizer such as one described above, an angle between an optical axis of the projecting section and each of the first synthesizing surface and the first exit surface is preferably in a range from about 40xc2x0 to 50xc2x0, most preferably 45xc2x0. Also, an angle between (a) the second light component after being received by the second receiving surface but before being synthesized with the first light component, and (b) the first light component after being received by the first receiving surface, but before being synthesized with the second light component, is preferably in a range from about 80xc2x0 to 100xc2x0, most preferably 90xc2x0. Finally, it is preferable that adjacent portions of the second exit surface and the second synthesizing surface are fixed to one another in such a way that they are free from air gaps.
A color synthesizing device according to another aspect of the present invention includes first, second, and third prisms, wherein the first prism includes a first receiving surface for receiving a first light ray from a first direction normal to the first receiving surface, the second prism includes a second receiving surface for receiving a second light ray from a second direction normal to the second receiving surface, and the third prism includes a third receiving surface for receiving a third light ray from a third direction normal to the third receiving surface. The first prism also includes a first exit surface for allowing the thus received first light ray to pass from the first prism to the second prism. The second prism also includes a first synthesizing surface for reflecting the thus received second light ray while receiving the first light ray from the first prism, thereby synthesizing the first and second light rays, and a second exit surface for allowing the thus synthesized first and second light rays to pass from the second prism to the third prism, wherein the second light ray is synthesized with the first light ray before striking the second exit surface. The third prism also includes a second synthesizing surface for reflecting the third light ray while receiving the synthesized first and second light rays from the second prism, thereby synthesizing the first, second, and third light rays, and a third exit surface for both reflecting the third light ray and allowing the synthesized first, second, and third light rays to exit from the color synthesizer.
In a color synthesizing device in accordance with the present invention such as the one described above, an angle between a direction normal to the third exit surface and each of the first synthesizing surface and the first exit surface is preferably in a range from about 40xc2x0 to 50xc2x0, most preferably 45xc2x0. An angle between (a) the second light ray after being received by the second receiving surface but before being synthesized with the first light ray, and (b) the first light ray after being received by the first receiving surface but before being synthesized with the second light ray, is preferably in a range from about 80xc2x0 to 100xc2x0, most preferably 90xc2x0. Also, it is preferable that adjacent portions of the second exit surface and the second synthesizing surface are fixed to one another in such a way that they are free from air gaps.
According to yet another aspect of the present invention, a projection display apparatus is provided that comprises a light source; a color separator for separating light from the light source into first, second, and third light components corresponding to three primary colors; first, second, and third transmission-type light valves for respectively modulating the first, second, and third light components; a color synthesizer for chromatically synthesizing the first, second, and third light components that have been respectively modulated by the transmission-type light valves; and a projecting section for projecting the thus synthesized light, wherein the color synthesizer comprises multiple prisms, first and second dichroic surfaces that have different wavelength selection characteristics from each other, and a prism surface that satisfies a total reflection requirement for the third light component, and wherein (i) the first dichroic surface is at a 40xc2x0 to 50xc2x0 angle relative to an optical axis of the projecting section, and is for chromatically synthesizing the first and second light components; (ii) the second dichroic surface is for chromatically synthesizing the first and second light components, which have been synthesized by the first dichroic surface, as well as the third light component that has been totally reflected by the prism surface; and (iii) the first, second, and third light components, which have been synthesized by the first and second dichroic surfaces, exit through the prism surface.
A projection display apparatus according to another embodiment of the invention comprises a light source; a light separator for separating light from the light source into first, second, and third light components corresponding to three primary colors; first, second, and third reflective light valves for respectively modulating the first, second, and third light components; a color synthesizer for chromatically synthesizing the first, second, and third light components that have been modulated by the respective reflective light valves; and a projecting section for projecting the thus synthesized light, wherein the color synthesizer comprises multiple prisms, first and second dichroic surfaces that have different wavelength selection characteristics from each other, and a prism surface that satisfies a total reflection requirement for reflecting the third light component, wherein (i) the first dichroic surface is at a 40xc2x0 to 50xc2x0 angle relative to an optical axis of the projecting section, and is for chromatically synthesizing the first and second light components; (ii) the second dichroic surface is for chromatically synthesizing the first and second light components, which have been synthesized by the first dichroic surface, as well as the third light component that has been totally reflected by the prism surface; and (iii) the first, second, and third light components, which have been synthesized by the first and second dichroic surfaces, exit through the prism surface.